The invention relates to a disc brake for a commercial vehicle, having a brake caliper which straddles a brake disc and is held on a stationary brake carrier such that it can be displaced in the brake application direction by way of guide bushings fastened to the brake carrier via screws.
In disc brakes of this type, which are also called sliding caliper brakes, the brake caliper is connected to a stationary brake carrier which is fastened to the vehicle. To this end, guide bushings are fastened to the brake carrier by use of screws and form plain bearings together with sliding bushings which are arranged in the brake caliper. The guide bushings are guided in the sliding bushings in such a way that an axial displacement of the brake caliper relative to the brake carrier is possible.
The guide bushing is manufactured from solid material, principally a round steel, and is machined with the removal of material, a small collar being formed on the end side which faces the brake carrier. This small collar is inserted into a stepped bore, adapted thereto, of the brake carrier, as a result of which centering of the guide bushing is achieved.
The centric middle hole of the stepped bore has a thread, into which the screw is screwed, which is guided with its shank through the bushing. The head of the screw is supported on the opposite side of the guide bushing. Here, a cheese head screw with a hexagon socket is preferably used, which cheese head screw is supported with its head on the bottom of the first step of the through hole of the guide bushing, which through hole is likewise configured as a stepped bore.
In addition to the above-mentioned material-removing forming of the small collar and the introduction of the through hole, the circumferential face of the guide bushing has to be prepared for functioning as a plain bearing, for example by way of grinding and/or thermal treatment in the case of a hardened embodiment.
Of the two plain bearings, one is configured as a locating bearing and the other is configured as a floating bearing in order to compensate for manufacturing-induced tolerances. This requires a multiplicity of variants of guide bushings and also a corresponding number of different screws.
This naturally leads to considerable manufacturing and/or stock keeping outlay with the resultant cost disadvantages which oppose an optimization of costs, as is always aimed for precisely in the case of series-produced products.
The invention is based on the object of developing a disc brake of the above-mentioned type in such a way that it can be manufactured and assembled less expensively using structurally simple means.
This and other objects are achieved by way of a disc brake for a commercial vehicle, having a brake caliper which straddles a brake disc and is held on a stationary brake carrier such that it can be displaced in the brake application direction by way of guide bushings fastened to the brake carrier via screws. The guide bushing are arranged parallel to and at a spacing from one another and form plain bearings, wherein each guide bushing is wedged with the associated screw. In this way, a disc brake is produced which can certainly be manufactured considerably less expensively than the known disc brakes.
First of all, a standardized, preferably seamless steel tube which is suitable for material-removing machining and thermal treatment can be used as a guide bushing.
The omission of the introduction of a through hole into the guide bushing results not only in manufacturing advantages, but also in a saving of material.
The wedging, provided according to the invention, of the guide bushing with the screw makes it possible to use identical screws for the different uses, which likewise contributes to an optimization of costs, such as just one embodiment for all guide bushings. In particular, stock keeping both of screws and guide bushings is simplified considerably.
The semifinished product of the guide bushing, which is present as a tube, can be dimensioned in such a way that hardening followed by thermal treatment and subsequent grinding of the circumferential face within the predefined low tolerances are possible.
The wedging of the guide bushing on the screw preferably takes place by way of a wedge sleeve, with an inner face which rises in the screwing direction, whereas the outer circumferential face, which bears against the inner wall of the guide bushing, is kept cylindrical.
In order to produce the wedging action, that is to say in order to spread open the wedge sleeve, the latter is slotted continuously in the axial direction, the head of the screw, which head is adapted to the oblique face of the inner face of the wedge sleeve at least over a partial height, ensuring a spreading and wedging action with the guide bushing when screwed in.
According to a further aspect of the invention, the wedge sleeve is rolled as a sheet metal part from a strip and is either pressed into the guide bushing or is placed into it with play.
Depending on the design of the taper ratio between the head of the screw and the wedge sleeve, a self-securing clamping action is achieved. This leads to a radial expansion of the guide bushing when a defined radial clamping force is achieved. As a result, pressing onto the wall of the receiving bore of the brake carrier takes place, in which receiving bore the guide bushing lies on the end side.
According to one variant of the invention, the guide bushing can have a radially inwardly drawn circumferential collar in the end side region which faces the brake carrier as an axial abutment, on which the wedge sleeve is supported.
According to another embodiment, the abutment is formed by the bottom of the brake carrier-side stepped bore, in the first step of which the guide bushing lies. In this case, the wedge sleeve is pressed into the guide bushing, with the result that a captive securing means is produced which affords assembly advantages.
Since the wedge sleeve is arranged in the connecting region with the brake carrier, and accordingly the head of the screw is also positioned here, the screw can be kept considerably shorter than one according to the prior art, which likewise has a cost-reducing effect.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.